Diamond grinding layer for honing segments

ABSTRACT

A diamond grinding layer, particularly suitable for honing segments comprising a porous metal carrier, a binding metal filling at least partially the pores of said carrier and diamond grinding grains, the metal carrier being composed of hard metal powder, a bonding metal powder and non metallic destruction particles, the metal carrier having wear properties substantially the same as the diamond grinding grains.

United States Patent [191 Sejbal et al.

DIAMOND GRINDING LAYER FOR HONING SEGMENTS Inventors: Josef Sejbal; Frantisek Curn, both of Praha, Czechoslovakia Assignee: Naradi, Narodni Podnik, Praha,

Czechoslovakia Filed: Sept. 8, 1971 Appl. No.: 178,847

Related US. Application Data Continuation-in-part of Ser. No; 139,937, May 3, 1971, abandoned.

Foreign Application Priority Data 3,820,966 1 June 28, 1974' [56] References Cited UNITED STATES PATENTS 2,137,329 11/1938 Boyer 51/309 2,240,829 5/1941 Bevillard 51/309 2,277,428 3/1942 Engle 51/309 2,607,676 8/1952 Kurtz 51/309 3,178,273 4/1965 Libal 51/309 3,594,141 7/1971 Houston et a1. 51/309 Primary ExaminerDonald J. Arnold Attorney, Agent, or FirmMurray Schaffer [57] ABSTRACT A diamond grinding layer, particularly suitable for honing segments comprising a porous metal carrier, a binding metal filling at least partially the pores of said carrier and diamond grinding grains, the metal carrier being composed of hard metal powder, a bonding metal powder and non metallic destruction particles, the metal carrier having wear properties substantially the same as the diamond grinding grains.

1 Claim, No Drawings pending application, U.S.S.N.

7 BACKGROUND OF THE INVENTION This application is a continuation-in-part of our co- 139,937 filed May 3, 1971 and now abandoned.

It is an object of this invention to provide a diamond grinding layer for honing segments.

It is a further object of the invention to provide adiamond grinding layer comprising diamond grinding grains embedded in a porous metallic carrier and in which the pores are filled at least partially by a binding metal.

It is still another object of the invention to provide a diamond grinding layer suitable for use as honing seg ments which, despite higher costs, is economically more advantageous due to improved longevity.

Present attempts to develop, particularly for series and mass production a diamond grinding layer suitablefor use as honing segments and which despite higher costs is economically more advantageous than those now generally known and which employs corundum, that is, alumina, grinding layers, have not been particularly successful. Among the advantages of diamond grinding layers is their longer life, so that costs of frequent adjustment and change of the honing segments are reduced. This is a great advantage where the honing segment is part of a manufacturing line. The longevity of diamond grinding layers depends on a suitable structure and composition with respect to the grinding layer and is particularly influenced by a suitable composition with regard to the binding means. Metals are generally used as binding means because of their good thermal conductivity and their good mechanical properties.

Known diamond grinding layers which employ a metal binder can be divided into three groups according to their structure.

The first group includes. diamond grinding layers which have a homogenous metal binder, manufactured usually by casting and in which the diamond grinding grains are cast in a suitable binding metal such as bronze.

The second group includes diamond grinding layers having diamond grinding grains embedded in a metal carrier obtained by sintering metal powder, generally carbides of metals and cobalt.

The third group includes diamond grindinglayers where the diamond grinding grains are embedded in a porous metallic carrier made by sintering metal powders, whereby the pores of the metallic carrier are filled with a binding metal, for instance such as silver solder or bronze. Iron powders. cobalt and other similar materials can also be used for this purpose. a

A drawback of diamond grinding layers of the first group is the fact that the relatively soft metal binder is rubbed out by particles of the worked material and the diamond grinding grains are broken out too early and thus are not fully utilized, resulting in a relatively short lifefor this grinding layer. A drawback of diamond grinding layers of the second group is the too rigid embedding of diamond grinding grains in the metal carrier. The metal carrier is very rigid and hard so that it is not rubbed out, but the active grinding surface is clogged by particles of the worked materiaL'thereby increasing the cutting resistance and reducing the removal of material to a minimum. It is therefore necesmetal and higher than 450 sary to interrupt the honing process from time to time and mechanically or chemically clean the active surface of the grinding layer in order to free further the unwom diamond grinding grains.

Diamond grinding layers of the third group are the most advantageous, but even in this group a uniform reduction of the'binding metal and of the metal carrier which depends on the wear of the diamond grinding grains is not achieved, so that the longevity of these grinding layers does not surpass thecurrent average,

When using current corundum, that is, alumina grinding layers, an average of 2,000 worked openings, for instance on combustion engine cylinders, is achieved. Diamond grinding layers have an average life of 3,000 to 5,000 worked openings for grinding layers of the first group and 7,000 to 10,000 worked openings for grinding layers of the second and third group. The diamond grinding layers achieve therefore as much as five times the life time of corundum grinding layers, but the cost of a diamond grinding layer with respect to the corundum layer is about sixty times higher, so that even the maximum achieved life time of diamond grinding layers is still too low.

SUMMARY OF THE INVENTION It is an object of this invention to .overcome the drawbacks mentioned and to increase the life and efficiency of diamond grinding layers. According to this invention, a porous metal carrier is made of a mixture of a hard metal power, the hardness of which is higher than 150 HB, of a bonding metal powder; the melting temperature of which is higher than 1,400 C. and lower than l,600 C. and of non-metallic destruction particles, the hardness according to Mohs is higher than 7 and wherein the pores of the metal carrier are at least partially filled with a binding metal, the melting temperature of which is lower than that of the bonding C. The thus prepared diamond grinding layer comprises 10 to 60 percent by volume of hard metal powder, 1 to percent by volume of bonding metal powder, 0.5 to 25 percent by volume of nonmetallic destruction particles, 15 to 60 percent by volume of binding metal and 5 to 25 percent by vol ume of diamond grinding grains, the remainder of the whole volume being free pores of the metal carrier.

DESCRIPTION OF PREFERRED EMBODIMENT As hard metal powder there can be used niobium, tantalum, titanium, molybdenum vanadium and tungsten powder, their nitrides and borides, and the like. Similarly, mixtures of these such as a mixtureof tungsten with carbide of Wolfram and the like can also be utilized. As bonding metal, iron,nicl e| and cobalt powders can be used. Non-metallic destruction particles include advantageously boron carbide, aluminium oxide or silicon carbide powder or the like. Binding metals include for instance copper, zinc, tin, silver or cadmium and their alloys and the like.

According to this invention, a substantially three stage structure in connection with the metal carrier is provided. The invention succeeds in combining the favorable properties of diamond grinding layers having a soft metal binding agent and in which the binding agent has good sliding properties and wears away at a subvorable properties of diamond grinding layers having a metal carrier made from sintered carbides, that is, one in which a rigid embedding of the diamond grinding grains in the sintered carbide takes place in the course of the cutting process. The admixture of non-metallic destruction particles to the porous metal carrier has of course to result in its destruction in due time. An optimum removal of the binding agent proportional to the wear of diamond grinding grains can be achieved by a suitable dosing of the non-metallic destruction particles. ln accordance with the invention, high utilization of the diamond raw material together with a uniform removal of the binding agent results in an extraordinary long life for the diamond grinding layer which could not be heretofore achieved and the necessity of treating, working or repairing of the active surface of the grinding layer in the course of the honing process is essentially eliminated.

Tests have proved that the assumptions on which the arrangement of our diamond grinding layer is based are correct. Tests performed independently on different working sites proved that the life time of a diamond grinding layer according to this invention surpasses 20,000 worked openings. In some cases where linings of compressor cylinders and openings in covers of electric motors have been honed, over 10,000 honed openings have been achieved.

In order to illustrate the invention more fully, the following illustrated examples are given. lt is to be understood that theexamples are illustrative only and not limitative. In the examples all parts and percentages are by weight unless otherwise stated.

EXAMPLE 1 An exemplary composition of a diamond grinding layer suitable as a honing segment for roughing operations indicated in volume percentage is: 33.25% WC, 1.75% Co, 6.25% 8 C, 40% alloy Cu Sn 20 and 16.25% of 30 micron diamond grinding grains, the rest of the whole volume being free pores ofthe metal carrier. The diamond grinding layer surpas'sed 20,000 worked openings.

EXAMPLE 2 An exemplary composition of a diamond grinding layer suitable as a honing segment for finishing operations indicated in volume percentage is: 38.95% W, 2.05% Ni, 10.5% A1 35% of alloy Ag 50, Cu Sn and 12.5% of 200 microns diamond grinding grains, the remainder of the entire volume being free pores of the metal carrier. The diamond grinding layer surpassed 100,000 honed openings.

The size of grains of the hard metal powder is generally advantageously less than 60 microns, the size of grains of the binding metal powder should be equally less than 60 microns, the size of destruction particles should be smaller, generally, from about two to four 4. grain sizes lower than the first mentioned particles. The size of the diamond particles depends on the requirements of the finished surface and can be from about 30 microns to 200 microns, in most cases microns.

The manufacture of a diamond grinding layer according to this invention can proceed in a variety of different ways.

One method of preparation is to mix the above mentioned ingredients and press them to the required shape, after which heat is applied to cause sintering. The applied heat should be below the melting point of the bonding metal and above the melting point of the binding metal.

A second method of preparation is to apply pressure and heat simultaneously.

A third method of preparation is to first press the hard metal powder, the bonding metal, the destruction particles and diamond grains so that some pores still remain in the pressing. These pores are subsequently filled by heating in an inert atmosphere with the binding metal, which infiltrates into the pores and causes diffusion with the particles of the carrier.

This raw product is then treated with a grinding material of a lower hardness than that of diamonds in order to uncover the diamond particles on the surface of the grinding layer as is generally done with similarly produced grinding tools.

Numerous advantages of this invention will be apparent. Moreover, it is to be understood that this invention is not to be limited except as defined in the appended claims.

What is claimed is:

1. Diamond grinding layer, particularly for honing segments, comprising in volume percent, based on the total volume, 5 to 25 percent diamond grinding grains embedded in a metallic carrier comprising 10 to 60 percent of porous hard metal powder particles which have a hardness greater than HB and are selected from the group consisting of niobium, tantalum, titanium, molybdenum, vandium and tungsten, and their nitrides, borides and carbides and mixtures thereof, 0.5 to 25 percent of non-metallic destruction particles having a hardness higher than 7 on the Mohs scale and which are selected from the group consisting of boron carbide, aluminum oxide and silicon carbide, 1 to 70 percent of a bonding metal powder a melting temperature higher than 1,400C. and lower than 1,600C. and which is selected from the group consisting of iron, nickel and cobalt and 0.15 to 60 percent of a bonding metal having a melting point between about 450C. and the melting point of the bonding metal and which is selected from the group consisting of copper, tin, zinc, silver cadmium and alloys thereof and which is disposed in and fills some of the pores of said metal carrier. 

